There are two main types of increased hair growth: (1) hirsutism, which is defined as the presence of excess terminal hair in women only and in anatomic sites where hair growth is considered to be a secondary male characteristic (i.e. beard, moustache, chest, and midline of lower abdomen primarily) and under androgen control and (2) hair density or length beyond the accepted limits of normal in a given body area for a particular age, race, and gender (hypertrichosis). Hypertrichosis may be in one or many areas and of terminal, vellus, or lanugo hair and is not under androgen control. Terminal hair is defined as hair that is similar in diameter to hair growing on the occipital scalp or eyebrows and usually >40 μm in diameter but its maximum length is body site dependent. Vellus and lanugo hair are of diminished diameter and color compared to terminal hair and do not grow beyond several centimeters in maximum length. Both types of increased hair growth can occur secondary to inherited conditions or can occur secondary to the use of certain medications. Hirsutism can be caused by the use of exogenous androgens or medications that bind to the androgen receptor (some progestins and anabolic steroids, for example) and diffuse hypertrichosis can be caused by the use of certain systemic drugs (minoxidil, diazoxide, cyclosporine, for example). Local hypertrichosis can be caused by the use of certain topical drugs, such as prostaglandin F analogs used for glaucoma and topical minoxidil used for hair growth in male or female pattern baldness. In addition, there are situations where the hair growth is determined to be within normal limits for a given ethnic group but increased in comparison with the general population. In some cases the excess hair growth can be desirable (i.e. in eyelashes) but in general, increased hair growth, especially in women, is viewed as undesirable and various means are utilized to remove the unwanted hair. There are also situations where the amount of hair is not indicative of hypertrichosis or hirsutism but the subject finds the amount of hair or the frequency of removal undesirable.
The current means of treating both hirsutism and hypertrichosis include physical means of hair removal including shaving, laser hair removal, electrolysis, depilatories, and waxing. These methods all require repetitive treatments, and none ensure complete and lasting hair removal, particularly in the presence of a continued systemic abnormality that is driving a vellus to terminal transition of hair. Currently, there is one FDA approved medication that slows hair growth: a topical omithine decarboxylase inhibitor Eflornithine (Vaniqa®) that shows significant efficacy in only a limited proportion of women with unwanted facial hair and has not been proven safe to use on other, larger body surface areas. There are several systemic agents that slow the transition of vellus to terminal hair growth or cause some miniaturization of terminal hair in women with hirsutism, and these agents include systemic antiandrogens (such as spironolactone, flutamide, and cyproterone acetate) and 5α-reductase inhibitors (such as finasteride or dutasteride). However, these agents do not cause total removal of the unwanted hair nor are they FDA approved for this indication. In addition, these systemic agents all have the risk of feminization of a male fetus in women of child-bearing potential and possibly other side effects as well. All of these methods, topical or systemic, require the continued use of other agents to remove unwanted hair. Thus there is a need for new products that work in a higher percentage of patients with unwanted hair, including those caused by hypertrichosis or hirsutism, and/or have fewer and less severe side effects.
Another unmet need is the alteration or prevention of pigmentation in the hair or skin. There are conditions where the skin may have too much pigmentation where inhibiting the pigmentation could be of value to patients. When used to alter or prevent pigmentation in the hair or skin, the compounds are applied in the same manner as for inhibition of hair growth, but the concentration or application may differ as needed.
Another unmet need is chemotherapy- or radiation-induced hair loss, particularly that occurring in women. Many cytotoxic chemotherapeutic agents or radiation that target rapidly growing cancer cells inadvertently also affect the rapidly growing anagen hair matrix cells, causing a profound and psychologically debilitating hair loss. This hair loss may make women in particular choose alternate therapies that do not cause this adverse effect, and/or it may cause a great deal of depression and/or anxiety during the entire cancer treatment process.
Prostaglandins have been shown in vivo to increase hair length and pigmentation. Naturally occurring prostaglandins (e.g., PGA2, PGB2, PGE1, PGE2, PGF2α, and PGI2) are C-20 unsaturated fatty acids. PGF2α, the naturally occurring Prostaglandin F (PGF) analog in humans, is characterized by hydroxyl groups at the C8 and C11 positions on the alicyclic ring, a cis-double bond between C5 and C6, and a trans-double bond between C13 and C14. PGF2α has the formula:

Analogs of naturally occurring Prostaglandin F are known in the art. For example, see U.S. Pat. No. 4,024,179 issued to Bindra and Johnson on May 17, 1977; German Patent No. DT-002,460,990 issued to Beck, Lerch, Seeger, and Teufel published on Jul. 1, 1976; U.S. Pat. No. 4,128,720 issued to Hayashi, Kori, and Miyake on Dec. 5, 1978; U.S. Pat. No. 4,011,262 issued to Hess, Johnson, Bindra, and Schaaf on Mar. 8, 1977; U.S. Pat. No. 3,776,938 issued to Bergstrom and Sjovall on Dec. 4, 1973: P. W. Collins and S. W. Djuric, “Synthesis of Therapeutically Useful Prostaglandin and Prostacyclin Analogs”, Chem. Rev. Vol. 93 (1993), pp. 1533-1564; G. L. Bundy and F. H. Lincoln, “Synthesis of 17-Phenyl-18,19,20-Trinorprostaglandins: I. The PG Series”. Prostaglandin, Vol. 9 No. 1 (1975), pp. 1-4; W. Bartman, G. Beck, U. Lerch, H. Teufel, and B. Scholkens, “Luteolytic Prostaglandin: Synthesis and Biological Activity”, Prostaglandin, Vol. 17 No. 2 (1979), pp. 301-311; C. liljebris, G. Selen, B. Resul, J. Sternschantz, and U. Hacksell, “Derivatives of 17-Phenyl-18,19,20-trinorprostaglandin F2α. Isopropyl Ester: Potential Antiglaucoma Agents”, Journal of Medicinal Chemistry, Vol. 38 No. 2 (1995), pp. 289-304.
Prostaglandins in general have a wide range of biological activities. For example, PGE2 has the following properties: a) regulator of cell proliferation, b) regulator of cytokine synthesis, c) regulator of immune responses and d) inducer of vasodilatation. Vasodilatation is thought to be one of the mechanisms of how minoxidil provides a hair growth benefit. In vitro results in the literature also indicate some anti-inflammatory properties of the prostaglandins. c.f.; Tanaka, H. Br J. Pharm. (1995) 116, 2298.
However, previous attempts at using prostaglandins to inhibit hair growth have been unsuccessful. Although different prostaglandin analogs can bind to multiple receptors at various concentrations, they have a biphasic effect. Further, the ability of the various in vitro animal models to predict human efficacy data has been poor. Certain animals have different receptors in different tissues, and even those that have similar receptor patterns may have different relative levels of receptors for prostaglandins. This makes evaluating the animal data to predict human efficacy challenging.